Molded metal castings are commonly manufactured at foundries through a matchplate molding technique which employs green sand molds comprised of prepared sand and additives which are compressed around cope and drag patterns mounted on opposite sides of a matchplate. The sand mold is thus formed in upper and lower matching portions, an upper cope mold, and a lower drag mold. The cope mold is formed in a separate cope flask which is filled with prepared sand and compacted onto the matchplate. The matchplate is then removed leaving an indentation in the cope mold of the desired shape for the upper portion of the casting. Simultaneously, the drag mold is formed in a separate drag flask. Usually the matchplate is in the form of a planar member with the pattern for the cope mold on one side and the pattern for the drag mold on the other. After the cope and drag molds have been formed, they are placed together to form a unitary mold having an interior cavity of the desired shape. The cavity can then be filled with molten metal through an inlet or "sprue" provided in the cope mold to create the desired casting. Such a system is disclosed in Hunter U.S. Pat. No. 5,022,212.
As with many volume sensitive production operations, manufacturers are required to automate the manufacturing process in order to remain competitive. Foundries engaging in the casting of metal objects through the use of green sand molds are not immune to this reality. It is common in today's marketplace, for the machine which produces the sand molds to be connected to a machine which fills the sand mold with molten metal, which in turn is connected to a machine for cooling the molten metal into a solid casting, which in turn is connected to a machine for removing the sand mold and revealing the casting for harvest. Such a system is disclosed in Hunter U.S. Pat. No. 4,589,467.
In the aforementioned '467 patent, the sand molds are manufactured and communicated along a linear conveyor to a circular, rotating, or "carousel" conveyor. Molten metal is introduced into the molds at one location on the carousel and the molten metal is then allowed to cool within the sand mold as the carousel rotates. The carousel is provided with both an outer diameter track and an inner diameter track which provide for additional cooling of the metal, and which increase the throughput of the machine.
While such a carousel system has enjoyed, and continues to enjoy, considerable commercial success, it is not without its drawbacks. In particular, if a manufacturer wishes to increase the throughput of a carousel-type molding machine, a carousel of a different diameter will necessarily have to be employed, at considerable additional expense. In addition, every time a new carousel is needed, a substantial down-time period is encountered wherein the machine is not producing castings, and which requires considerable labor to put into effect.
Similarly, if the cooling times of the metal being processed through machine are variable, the length of the cooling cycle will accordingly be affected. With a carousel-type conveyor, the cooling cycle time can be increased either by slowing the carousel, or by adding a carousel of a greater diameter. Conversely, if the cooling time is to be lessened, the rotational speed of the carousel can be increased, or a carousel having a smaller diameter can be added. However, both options are less than desirable. If the carousel is slowed, the throughput of the machine is proportionally diminished, and if a new carousel is added, additional expense is incurred due to increased downtime and additional equipment overhead.
Co-pending U.S. patent application Ser. No. 08/783,647 therefore discloses a linear mold handling system wherein separate double-deck pouring and cooling conveyors are provided. Sand molds are transferred to the pouring conveyor and indexed to a station in which molten metal is deposited into the sand molds. The molten metal filled sand molds are then transferred to a lower level of the pouring conveyor and then back to the upper level of the pouring conveyor before being transferred to a separate cooling conveyor provided laterally adjacent to the pouring conveyor. The embodiment disclosed in the aforementioned parent application provides a cooling conveyor which is three rows wide and includes a plurality of trays adapted to receive up to three molds disposed on the conveyor. The partially cooled sand molds are transferred from the pouring conveyor to the cooling conveyor and into one of the trays disposed thereon. Each tray is adapted to receive up to three sand molds. Once a tray is filled, it is indexed forward until reaching an end of the upper level of the cooling conveyor at which time the elevator lowers the trays to a lower level and then back to an upper level of the cooling conveyor before being pushed into a dump chute and a shake-out vibrating conveyor.
However, depending on the particular metal being poured differing dwell times will be required for adequate cooling of the poured metal. In certain instances, it may not be necessary to provide four complete rows for cooling of the metal. In addition, since such an embodiment employs completely separate pouring and cooling conveyors, dual sets of conveyors, elevators, controls, and the like are required which necessarily result in added expense, maintenance and complexity.